An inductor is an electrical device that introduces inductance into a circuit or functions by inductance within a circuit. In some applications, it is useful for inductors to be tunable. For example, circuits designed for RF applications may benefit by using tunable inductors. In particular, tuned circuits that include LC tanks used for loads, filters, impedance matching, or the like may use tunable inductors for tuning center frequencies.
The center frequency of an LC tank may be tuned for various reasons. For example, tuning the center frequency of LC tanks may compensate for process variation. In other cases, tuning the center frequency may track a signal frequency that varies. In addition, tuning the center frequency of an LC tank can produce a particular amplitude or phase for a given frequency.
A tunable inductor, having an inductance that may be controlled manually or automatically, typically is tunable only by mechanical means. Variable capacitors, also known as varactors, are sometimes used to tune LC tanks. If a varactor is grounded, banks of switched capacitors may be necessary to properly tune an LC tank.